This invention relates to a method for twisting individual strands of yarn and plying these individually twisted strands around each other, and the yarn made according to the method. More specifically, this twisting action is accomplished by false-twisting, where for a certain yarn length the yarn is twisted a number of turns in one direction and then for another sequential length, it is twisted in the opposite direction. The application also discloses yarns produced according to the method and on an apparatus of the type described.
The nature of false twisting is such that the total number of turns in one direction minus the total number of turns in the opposite direction over the total yarn-length is zero. The method of taking several twisted yarns and combining them by twisting them together to make a multi-stranded yarn has been known for thousands of years. However, plying previously-twisted yarns together is energy and time-consuming, since for every turn in the individual yarn and also for every turn in the plied multi-stranded yarn, the yarn packages must be turned around their axis.
The apparatus and method according to the invention is much more economical since only a relatively short piece of each yarn is twisted around its own axis. The secondary plying occurs automatically since, through the inserted torque, the twisted yarns in the single yarn twist around each other in the direction of the yarn-torque.
The false-twist process requires that care be taken to insure that the false-twisted multi-stranded yarn does not untwist at the place of twist-reversal. This is normally accomplished by attaching fibers of a single yarn to fibers of another, adjoining yarn. Various means of interlocking of these yarns at the twist reversal places have been used, for example, intermingling the fibers through abrasion, ultrasonic bonding, intermingling the fibers with an air-jet directing high-pressure air onto the traveling yarn, for example.